The problems in sleep medicine caused by the cost; access and variety of sleep laboratory testing have led to increasing use and demand for home testing particularly for evaluation of suspected sleep apnea. The definition of sleep-related breathing disorders (SRBD) has, however, expanded to include flow-limited breathing events. Assessment of these events and of hypopneas requires quantitative analyses of the airflow not provided by thermal sensors. Nasal air pressure, however, provides a quantitative measurement of airflow sufficiently accurate to detect both hypopneas and flow-limited breaths. In this project an untethered, miniature, self-applied ambulatory unit (AirTrac) will be built to measure airflow from nasal pressure and record data for PC download. The AirTrac will detect apneas, hypopneas and flow-limited breaths and provide basic event rates and visual data display on the PC. In phase I a prototype system was developed and found to produce results similar to that of a polysomnogram. In phase II automatic data analyses programs will be integrated into the monitor and the system tested in clinical trials. This device could facilitate clinical screening and treatment evaluations for SRBD as part of the continuum of care in sleep medicine and could also expand opportunities for clinical research.